The present invention relates generally to processes for measuring the roughness of a surface and, more particularly, to a process and apparatus for photoelectrically measuring surface roughness of the inside surface of cylindrical tubing.
On machined surfaces requiring a high degree of smoothness such as in mirrors and lenses, semi-conductor wafers, etc., optical detection systems are known for detecting and photoelectrically measuring surface defects or "rough spots". For example, U.S. Pat. 4,030,830 discloses an optical detection system for detecting surface roughness of flat surfaces by converging a laser beam on selected areas of the surface. Back scattered light radiation is measured photoelectrically to provioe an indication of surface roughness. Because the surface is flat, it is possible to tilt it to separate specular reflection from back scattered radiation to produce a back scattered radiation signal using appropriate electronics.
To measure surface roughness of curvilinear surfaces, such as the inside cylindrical surface of metal tubing, different apparatus are employed, such as the device disclosed in U.S. Pat. 4,440,496 to Milana wherein the device is located within the tubing and is translated to analyze the surface by examination of a diffraction pattern generated by laser radiation normal to the surface. Other devices also requiring placement within tubing to examine cylindrical surfaces thereof are disclosed in U.S. Pat. Nos. 3,337,314 and 4,317,632.
Since the aforesaid prior art devices used to detect roughness in tubing must be moved along the inside cylindrical surface, such devices are not practical in examination of metal tubing having small internal diameters (e.g., 1 to 1.5 mm). Also, the aforesaid prior art devices are relatively expensive to manufacture and require expensive equipment supporting their movement within the tubing.